Removing heat from integrated circuit devices mounted on a support structure

ABSTRACT

A cover, acting as a heat sink for integrated circuit devices, encloses one or more devices mounted on a support structure. The thermally conductive cover is formed of a thermally conductive material and is also sealed to the support structure. By thermally contacting the cover to the integrated circuit devices, heat is dissipated from the integrated circuit devices. A thermally conductive paste can be applied between the cover and integrated circuit devices to facilitate heat transfer from the integrated circuit devices to the cover.

This is a divisional of prior application Ser. No. 09/023,315 filed Feb.13, 1998.

BACKGROUND

The invention relates to removing heat from integrated circuit devicesmounted on a support structure.

Integrated circuit devices, such as microprocessors, DRAMs, and ASICsmay contain millions of transistors. These integrated circuit devices,which may be bare dies mounted directly on a support structure (e.g.,printed wiring boards or ceramic boards) or encapsulated in plasticpackages, generate large amounts of heat during operation. Heatincreases a device's electrical resistance which slows down the deviceand may affect the device's overall performance. Heat also accelerateswear and tear on the device and may reduce a device's overall lifeexpectancy. Metal can also cause corrosion of metal liners used in theintegrated circuit. Therefore, it is desirable to remove heat fromintegrated circuit devices and generally keep them as cool as possibleduring operation.

Integrated circuit devices are also very moisture sensitive. Extendedexposure to humidity from the air may allow moisture to seep into thedevices and damage them. For example, moisture seeping underneath theprotective overcoat (PO) of an integrated circuit device will cause thePO to delaminate. Therefore, it is desirable to encapsulate integratedcircuit devices in hermetically sealed packages to protect them frommoisture. The packages also protect integrated circuit devices fromdamage due to physical stress during assembly and testing.

SUMMARY

In general, in one aspect the invention relates to a method for removingheat from an integrated circuit device mounted on a support includingmounting a thermally conductive cover with a thermally conductive heatdissipating fin structure on the support over the integrated circuitdevice. The cover is positioned over the integrated circuit device inheat conductive communication with the integrated circuit device. Athermally conductive layer is applied between the cover and theintegrated circuit device. The cover is attached to the support toprovide a hermetic seal.

In general, in another aspect the invention relates to a method forremoving heat from a plurality of integrated circuit devices mounted ona support including mounting a thermally conductive cover on the supportover a plurality of integrated circuit devices. The cover is positionedover the integrated circuit devices in heat conductive communicationwith the integrated circuit devices. A plurality of depressions areformed in the thermally conductive cover such that,the depressions arein heat conductive communication with corresponding integrated circuitdevices.

In general, in another aspect the invention relates to a moduleincluding a support structure. An integrated circuit device is mountedto the support structure. A thermally conductive cover, including heatdissipating fins, is attached to the support structure in heatconductive communication with the integrated circuit device.

In general, in another aspect the invention relates to an apparatus forremoving heat from an integrated circuit device mounted to a supportstructure. The apparatus includes a thermally conductive cover mountedon a support structure over the integrated circuit device. The cover hasa first surface that is adapted to be in heat conductive communicationwith the integrated circuit device. The cover further includes heatdissipating fins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged vertical cross-sectional view of a flip-chipassembly having a thermally conductive cover with fins;

FIG. 2 is an enlarged vertical cross-sectional view of an assemblyhaving multiple flip-chips enclosed by a thermally conductive cover; and

FIG. 3 is an enlarged vertical cross-sectional view of an assemblyhaving multiple chips-on-board enclosed by a thermally conductive cover.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the figures, common elements are identified with the same referencenumerals. As used in this description, “support substrate” refers to anystructure on which integrated circuit devices, e.g., dies, packageddevices, can be mounted. Such structures include printed circuit boardsor semiconductor dies.

Referring now to FIG. 1, a flip-chip assembly has a thermally conductivecover 50 with a plurality of fins 55. The fins 55 protrude from an outertop surface 54 to provide a greater surface area from which heatgenerated by the die 10 inside the cover 50 can transfer quickly anddissipate. The fins can be metal formed or coated metal fins for betterheat dissipation. A bare, unencapsulated integrated circuit die 10 ismounted face down directly on a support substrate 20. This supportsubstrate could be a printed circuit board “PCB”, a multi chip module(“MCM”) or other ceramic glass, of semiconductor substrate. The term“flip-chip” comes from the face down, or flipped, orientation of theintegrated circuit die 10 on the support substrate 20. Metal bumps 12which could be composed, for example, of Pb, Sn, In, Ag (which may begold plated) are formed on bonding pads (not shown) of the die 10. Thebumps 12 can be made of a polymer, such as a metal-filled epoxy or athermoplastic compound. Matching solder pads (not shown) are formed onthe support substrate 20 for receiving the bumps 12. During assembly,the bumps 12 are attached to the solder pads of the support substrate 20to electrically connect the die 10 to the support substrate 20. Standardflip-chip attach processes can be employed for this purpose.

The thermally conductive paste layer 40 is applied between the top,inner surface 52 of the cover 50 and the top surface 11 of theintegrated circuit die 10. A thermoset epoxy 41 may be applied betweenthe cover 50 and the substrate 20 to adhere the cover 50 to thesubstrate 20 and form a hermetic seal between the cover 50 and thesubstrate 20 so that the integrated circuit die 10 resides within aninner enclosed space 51 of the cover 50. This protects the integratedcircuit.

A ring of thermoset epoxy 41 (or other adhesive materials) may beapplied underneath a bottom wall portion 33 of the cover 50 to adherethe cover 50 to a top surface 21 of the support substrate 20. Theadhesive ring layer 41 also serves to hermetically seal the die 10 inthe inner enclosed space 31 of the cover 50. Alternatively, the cover 30may be soldered to the support substrate 20 to adhere and hermeticallyseal the cover 50 to the support substrate 20. Other securementtechniques could also be used.

The cover 50 acts as a heat sink to remove heat from the integratedcircuit die 10. During operation, heat generated by the die 10 istransferred through the thermally conductive paste layer 40 and into thethermally conductive cover 50 where it is dissipated into the air. Asthe amount of heat dissipated through a body is directly proportional tothe body's surface area, the larger surface area of the cover 50 (thanthat of the die 10) improves heat dissipation.

Referring now to FIG. 2, an assembly having multiple flip-chips enclosedby a thermally conductive cover cap is shown. Multiple bare,unencapsulated dies 60, 70 are mounted face down directly on a supportsubstrate 80. The multiple dies 60, 70 may have the same or differentthicknesses. Bumps 62 electrically connect the die 60 to the supportsubstrate 80, and bumps 72 electrically connect the die 70 to thesupport substrate 80. A thermally conductive cover 90 mounted to thesupport substrate 80 covers and encloses the multiple dies 60, 70 withinan inner enclosed space 91 defined by the cover 90 and the supportsubstrate 80. The cover 90 provides multiple offset portions 93, 95which may be stamped from a single piece of metal. The offset portions93, 95 protrude into the inner enclosed space 91 of the cover 90 toreach the back surfaces 61, 71 of the dies 60, 70. The top,inner-surface 94 of the offset portion 93 makes thermal contact with aback surface 61 of the die 60 through a thermally conductive paste layer100, and the top, inner surface 96 of the offset portion 95 makesthermal contact with a back surface 71 of the die 70 through a thermallyconductive paste layer 101. Depending upon the thicknesses of the dies60, 70, the offset portions 93, 95 may be of same or different depths.

The cover 90 may be attached to a top surface 81 of the supportsubstrate 80 by applying an adhesive ring 102 or a solder ring (notshown) underneath the bottom wall 97 of the cover 90. The cover 90hermetically seals the dies 60, 70 which are mounted to the supportsubstrate 80.

Alternatively, if dies having substantially similar thicknesses aremounted on the support substrate 80 such that their back surfaces reachsubstantially the same height, a cover without offset portions can beused to enclose and seal the dies. Any small variation in height can becompensated for by varying the thicknesses of the thermally conductivepaste layer.

An added advantage of the cover 90 is that it provides a larger surfacearea to dissipate heat.

Referring now to FIG. 3, a plurality of bare, unencapsulatedchip-on-board (“COB”) integrated circuit devices 10 are mounted face updirectly on a substrate 20. The integrated circuit devices 10 may be ofsame or different thicknesses. Bond wires 31, which may be made of gold,are bonded to bonding pads on the integrated circuit devices 10 andsubstrate 20, and electrically connect integrated circuit devices 10 tothe substrate 20. Bonding may be accomplished by, for example,thermosonic bonding. A thermally conductive cover 40 is attached tosubstrate 20 and covers the plurality of integrated circuit devices 10.Better heat dissipation may be achieved because the cover acts as both aheat sink and a cover.

The cover 40 has a plurality of offset regions 42 formed therein, whichmay be stamped from a single piece of metal. A plurality of offsetregions 42 may be of same or different depths, and enable cover 40 to bein thermal contact with each one of plurality of integrated circuitdevices 10.

A thermally conductive paste 50 may be applied between a plurality ofoffset regions 42 and a plurality of integrated circuit devices 10. Thepaste 50 contacts both the plurality of offset regions 42 and theplurality of integrated circuit devices 10. A thermoset epoxy 60 may beapplied between cover 40 and substrate 20 to adhere the cover 40 tosubstrate 20 and form a hermetic seal between cover 40 and substrate 20.Alternatively, cover 40 may be soldered to substrate 20 to adhere andhermetically seal cover 40 to substrate 20.

It is to be understood that the embodiments described above are merelyillustrative of some of the many specific embodiments of the presentinvention. Other arrangements can be devised by one of ordinary skill inart at the time the invention was made without departing from the scopeof the invention.

What is claimed is:
 1. An apparatus for removing heat from a pluralityof integrated circuit devices mounted to a support structure, saidapparatus comprising: a thermally conductive cover mounted on thesupport structure over said plurality of integrated circuit devices,said cover including an upper and lower surface, each having acorrugated shape including a plurality of depressions formed in saidcover, each of said depressions being rectangular and having a bottomsurface, a top surface and four substantially transverse side wallsconnecting said bottom surface to said top surface; and said coveradapted to hermetically seal to said support structure to enclose saidintegrated circuit devices in a sealed enclosure with said bottomsurfaces in heat conductive communication with said integrated circuitdevices.
 2. The apparatus of claim 1 wherein said depressions are ofdifferent sizes.
 3. A method for removing heat from a plurality ofintegrated circuit devices mounted on a support, comprising: mounting aplurality of integrated circuit devices on a support; mounting athermally conductive cover on the support over said plurality ofintegrated circuit devices, said cover having an upper and a lowersurface said upper surface including a series of upward protrusionsbetween the integrated circuit devices, said protrusions extending awayfrom said devices and a plurality of cavities between said protrusionsover said integrated circuit devices, said lower surface including aplurality of depressions, each of said depressions being rectangular andhaving a bottom surface and four substantially transverse side wallsconnecting said bottom surface to the rest of said cover, saiddepressions in said lower surface being opposed to said cavities in saidupper surface; positioning said bottom surfaces in heat conductivecommunication with said devices; and sealing said cover to said supportso as to hermetically enclose said devices between said cover and saidsupport.
 4. The method of claim 3, wherein the integrated circuitdevices include a bare die mounted on the support in a flip-chipconfiguration.
 5. The method of claim 3, wherein the integrated circuitdevices include a bare die wirebonded to the support.
 6. The method ofclaim 3, wherein the integrated circuit devices include a packaged die.